The present invention relates to formulations used in biofouling control in industrial water systems. More specifically, the present invention relates to methods of preparing stable oxidizing bromine formulations and their use in biofouling control in industrial water systems.
While elemental liquid bromine is an effective biocide, its low solubility ( less than 4 g/100 g water), low boiling point (54.3xc2x0 C.), high vapor pressure (214 mm Hg at 25xc2x0 C.) and extreme corrosivity limit its use as a biocide in industrial applications. Another oxidizing bromine compound, bromate, has very little antimicrobial activity. Bromate is also very toxic to mammals and is a suspected carcinogen. Nonoxidizing inorganic bromine compounds, such as bromide, have little or no antimicrobial activity.
A mixture of an aqueous bromine solution and a bromine stabilizer has been used to generate stable oxidizing bromine compounds for use as a biocide. An unstabilized aqueous bromine solution is very acidic, unstable and emits very pungent bromine fumes. The concentration of stabilized hypobromite solution that can be made from liquid bromine, however, has been limited due to the low solubility of bromine in water.
It has also been suggested that, in addition to a bromine stabilizer, an oxidizer, such as hypochlorite, be added to activate the bromide to hypobromite. After the completion of the conversion of bromide to hypobromite, the hypobromite is stabilized by the addition of a halogen stabilizer, such as sulfamate. While this is an improved process with a higher level of oxidizing halogen content (around 14% as Br2), this process still requires the separate step of synthesizing sodium hypobromite (NaOBr) as a bromine source. NaOBr is known to be very unstable and will rapidly disproportionate to bromide and bromate, both of which have little or no antimicrobial activity. In addition, because sodium hypochlorite (NaOCl) is used as an activation agent, the concentration of stabilized product is limited by the available concentration of NaOCl.
Also known are methods of generating bromine for on-site use. Such processes involve electrolytically converting bromate into active bromine compounds such as bromine, hypobromous acid, hypobromite ion and hydrogen tribromide under acidic conditions. However, because the above process generates bromine for on-site use, methods or measures for optimizing bromine stabilization are not addressed.
Therefore, methods of generating higher concentrations of stable oxidizing bromine formulations in a safer manner are needed.
The present invention satisfies the aforementioned needs by providing a method of generating a stable oxidizing bromine compound which includes the steps of mixing an alkali or alkaline earth metal bromide and an alkali or alkaline earth metal bromate in water to provide an aqueous solution, cooling the solution to a temperature of less than 25xc2x0 C., preferably less than 20xc2x0 C. and more preferably less than 10xc2x0 C., and thereafter adding a halogen stabilizer to the solution, the halogen stabilizer being selected from the group consisting of Rxe2x80x94NH2, Rxe2x80x94NHxe2x80x94R1, Rxe2x80x94SO2xe2x80x94NH2, Rxe2x80x94SO2xe2x80x94NHR1, Rxe2x80x94COxe2x80x94NH2, Rxe2x80x94COxe2x80x94NHxe2x80x94R1 and Rxe2x80x94COxe2x80x94NHxe2x80x94COxe2x80x94R1 wherein R is a hydroxy group, an alkyl group or an aromatic group and R1 is an alkyl group or an aromatic group. Preferred halogen stabilizers include urea, thiourea, creatinine, cyanuric acids, alkyl hydantoins, mono or diethanolamine, organic sulfonamides, biuret, sulfamic acid, organic sulfamates and melamine. Sulfamic acid is the most preferred halogen stabilizer.
In an embodiment, the halogen stabilizer is added to the solution in a molar amount approximately equal to the combined molar amount of alkali or alkaline earth metal bromide and alkali or alkaline earth metal bromate.
In an embodiment, the step of adding the halogen stabilizer results in the solution having a pH of less than 2.
In an embodiment, the method comprises agitating the solution for a time period of greater than 5 minutes after the step of adding the halogen stabilizer.
In an embodiment, the method comprises adjusting the solution to a pH of greater than 13 through the addition of alkali or alkaline earth metal hydroxide after the step of adding the halogen stabilizer.
In an embodiment, the step of mixing the alkali or alkaline earth metal bromide and alkali or alkaline earth metal bromate further comprises mixing the alkali or alkaline earth metal bromide and alkali or alkaline earth metal bromate in a molar ratio of alkali or alkaline earth metal bromide:bromate of about 2:1.
In an embodiment, the method of the present invention provides a stable oxidizing bromine compound which includes the steps of mixing about 2 moles of alkali or alkaline earth metal bromide and about 1 mole of alkali or alkaline earth metal bromate in water to provide an aqueous solution, followed by the step of cooling the solution to a temperature of less than 10xc2x0 C., followed by the step of adding an acidic halogen stabilizer to the solution to lower the pH of the solution to less than 2, the acidic halogen stabilizer being selected from the group consisting of Rxe2x80x94NH2, Rxe2x80x94NHxe2x80x94R1, Rxe2x80x94SO2xe2x80x94NH2, Rxe2x80x94SO2xe2x80x94NHR1, Rxe2x80x94COxe2x80x94NH2, Rxe2x80x94COxe2x80x94NHxe2x80x94R1 and Rxe2x80x94COxe2x80x94NHxe2x80x94COxe2x80x94R1 wherein R is a hydroxy group, an alkyl group or an aromatic group and R1 is an alkyl group or an aromatic group. Preferred halogen stabilizers include urea, thiourea, creatinine, cyanuric acids, alkyl hydantoins, mono or di ethanolamine, organic sulfonamides, biuret, sulfamic acid, organic sulfamates and melamine. The acidic halogen stabilizer is added to the solution in a molar amount approximately equal to a combined molar amount of alkali or alkaline earth metal bromide and alkali or alkaline earth metal bromate, followed by the step of agitating the solution for a time period of greater than 5 minutes, followed by the step of adding an alkali or alkaline earth metal hydroxide to the solution to increase the pH of the solution to a level greater than 13.
In an embodiment, the method of the present invention provides a method of preparing a stable oxidizing bromine compound which includes the steps of preparing a caustic solution comprising a halogen stabilizer, water and an alkali or alkaline earth metal hydroxide, adding bromine to the solution while agitating the solution and cooling the solution.
In an embodiment, the halogen stabilizer is selected from the group consisting of Rxe2x80x94NH2, Rxe2x80x94NHxe2x80x94R1, Rxe2x80x94SO2xe2x80x94NH2, Rxe2x80x94SO2xe2x80x94NHR1, Rxe2x80x94COxe2x80x94NH2, Rxe2x80x94COxe2x80x94NHxe2x80x94R1 and Rxe2x80x94COxe2x80x94NHxe2x80x94COxe2x80x94R1 wherein R is a hydroxy group, an alkyl group or an aromatic group and R1 is an alkyl group or an aromatic group. Preferred halogen stabilizers include urea, thiourea, creatinine, cyanuric acids, alkyl hydantoins, mono or di ethanolamine, organic sulfonamides, biuret, sulfamic acid, organic sulfamates and melamine.
In an embodiment, the caustic solution has a pH greater than 13 after the addition of bromine.
In an embodiment, the step of adding bromine is further characterized as adding bromine in a molar amount approximately equal to the molar amount of halogen stabilizer and approximately equal to one-half of the molar amount of alkali or alkaline earth metal hydroxide.
In an embodiment, the solution is cooled to a temperature of less than 25xc2x0 C.
In an embodiment, the step of adding bromine is performed without exposing the bromine to air.
In an embodiment, an alkali or alkaline earth metal hydroxide is added to the solution after the addition of bromine to increase the pH of the solution above 13.
In an embodiment, the method of the present invention provides a method of preparing a stable oxidizing bromine compound in an aqueous solution which includes the steps of dissolving an alkali or alkaline earth metal bromate salt in water to form a solution, followed by the step of adding a halogen stabilizer to the solution, the halogen stabilizer being selected from the group consisting of Rxe2x80x94NH2, Rxe2x80x94NHxe2x80x94R1, Rxe2x80x94SO2xe2x80x94NH2, Rxe2x80x94SO2xe2x80x94NHR1, Rxe2x80x94COxe2x80x94NH2, Rxe2x80x94COxe2x80x94NHxe2x80x94R1 and Rxe2x80x94COxe2x80x94NHxe2x80x94COxe2x80x94R1 wherein R is a hydroxy group, an alkyl group or an aromatic group and R1 is an alkyl group or an aromatic group. Preferred halogen stabilizers include urea, thiourea, creatinine, cyanuric acids, alkyl hydantoins, mono or di ethanolamine, organic sulfonamides, biuret, sulfamic acid, organic sulfamates and melamine. Following the addition of the halogen stabilizer, bromine is added to the solution.
In an embodiment, a step of cooling the solution to a temperature of less than 25xc2x0 C., preferably less than 15xc2x0 C. and more preferably less than 10xc2x0 C., is performed simultaneously with the step of adding the bromine to the solution.
In an embodiment, the present invention provides an aqueous biocide solution containing a stable oxidizing bromine formulation. The solution comprises at least one oxidizing bromine compound selected from the group consisting of xe2x88x92SO3NHBr and xe2x88x92SO3NBr2 when sulfamate is used as the bromine stabilizer and a base in an amount sufficient to raise the pH of the solution to a level greater than 13.
In an embodiment, the base in the solution is an alkali or alkaline earth metal hydroxide.
It is therefore an advantage of the present invention to generate a stable oxidizing bromine solution using liquid bromine in a safe and efficient manner whereby no bromine fumes are generated.
It is another advantage of the present invention to generate a higher concentration of stabilized hypobromite without the need for a separate step for hypobromite generation.
Another advantage of the present invention is that it provides a method for generating water soluble solid stable oxidizing bromine compounds.
Still another advantage of the present invention is that it provides a method for generating stable oxidizing bromine compounds without unwanted by-products such as high levels of bromate.
Still another advantage of the present invention is that the method of the present invention does not generate chloride and therefore the method of the present invention provides stable oxidizing bromine formulations that are less corrosive.
Yet another advantage of the present invention is that it provides stable oxidizing bromine compounds that are safer to transport and that are non-acidic.
Yet another advantage of the present invention is that it generates stable oxidizing bromine compounds for biofouling control in industrial water systems that are more compatible with other water treatment chemicals than unstabilized oxidizing bromine compounds.
The industrial water systems include cooling water systems, cooling ponds, reservoirs, sweetwater applications, decorative fountains, pasteurizers, evaporative condensers, hydrostatic sterilizers and retorts, gas scrubber systems and air washer systems.
Another advantage of the present invention is that it provides an improved method of biofouling control in pulp and paper processing systems.
Another advantage of the present invention is that it provides an improved method of biofouling control occurring on the surfaces of equipment in contact with produced oil field waters.
Another advantage of the present invention is that it provides an improved method of biofouling control in a food processing system.
Yet another advantage of the present invention is that it provides improved biofouling control in a beverage processing system.
Still another advantage of the present invention is that it provides improved biofouling control in a recreational water system.
Another advantage of the present invention is that it provides an improved method of disinfecting a hard surface.
Another advantage of the present invention is that it provides an improved bleaching method for the laundering of soiled garments and for the manufacture of cellulosic materials.
And, another advantage of the present invention is that it provides an improved method of washing food items, such as fruit and other food items.
Other objects and advantages of the present invention will be apparent upon a review of the following detailed description and appended claims.
The present invention provides a plurality of formulations and methods for generating a wide concentration of stable oxidizing bromine compounds for biofouling control in cooling water and other industrial systems.
In an embodiment, the strategy employed by the present invention utilizes a mixture of alkali or alkaline earth metal bromide and alkali or alkaline earth metal bromate in water as the bromine source. Bromate also serves as an oxidizing agent. The molar ratio of bromide to bromate is optimally 2:1. The solution is then cooled to a temperature preferably of less than 25xc2x0 C. and even more preferably of less than 10xc2x0 C. An acidic stabilizer or acidic stabilizing solution, such as sulfamic acid, is then added to the solution to lower the pH of the solution to less than 2. Additional stabilizer is then added to achieve equal molar amounts relative to bromine for optimal stabilization. Without being limited by theory, the following reactions are believed to occur:
HOxe2x80x94SO2xe2x80x94NH2 greater than H++xe2x88x92Oxe2x80x94SO2xe2x80x94NH2xe2x80x83xe2x80x83(1)
2Brxe2x88x92+BrO3xe2x88x92+3H+ greater than 3HBrOxe2x80x83xe2x80x83(2)
HBrO+xe2x88x92Oxe2x80x94SO2xe2x80x94NH2 greater than xe2x88x92Oxe2x80x94SO2xe2x80x94NHxe2x80x94Br, xe2x88x92Oxe2x80x94SO2xe2x80x94NBr2,xe2x80x83xe2x80x83(3)
and other stable oxidizing bromine compounds
Since bromide, bromate and sulfamate co-exist in the resulting solution, reaction (1) to reaction (3) occurs sequentially with respect to each other. Without being limited by theory, the existence of an oxidizing bromine stabilizer and correct bromide to bromate ratio are believed to prevent the formation of bromine according to the following reaction:
5NaBr+NaBrO3+6Hxe2x88x92 greater than 3Br2+6Naxe2x88x92+3H2Oxe2x80x83xe2x80x83(4)
If reaction (4) were to happen instead of reaction (2), half of the raw bromine source would convert back to non-biocidal and non-oxidizing bromide according to reaction (5):
Br2+H2O greater than HBrO+HBrxe2x80x83xe2x80x83(5)
However, an analysis of products prepared in accordance with the present invention confirms that the reaction yield is higher than 50%. In fact, more than 80% of the bromine source was converted to oxidized bromine forms. Accordingly, the reaction yield of at least 80% was achieved.
The reaction time for reactions 1-3 at a pH of less than 2 ranges from 5 to 10 minutes with good agitation. If the product is not going to be used immediately, a strong base, such as NaOH, is added to raise the product pH to a level greater than 13 making the product thermally stable. During the pH adjustment, temperature control is important because the temperature increase by the heat generated from the acid-base reaction can cause the product to decompose. Accordingly, cooling may be necessary.
The product made with the above process has good thermostability and a high total available halogen concentration, as high as 34% as Br2.